std:: setlocale

The setlocale function installs the specified system locale or its portion as the new C locale. The modifications remain in effect and influences the execution of all locale-sensitive C library functions until the next call to setlocale . If locale is a null pointer, setlocale queries the current C locale without modifying it.

Parameters

Return value

Pointer to a narrow null-terminated string identifying the C locale after applying the changes, if any, or null pointer on failure.

A copy of the returned string along with the category used in this call to std::setlocale may be used later in the program to restore the locale back to the state at the end of this call.

Notes

During program startup, the equivalent of std :: setlocale ( LC_ALL , "C" ) ; is executed before any user code is run.

Although the return type is char * , modifying the pointed-to characters is undefined behavior.

Because setlocale modifies global state which affects execution of locale-dependent functions, it is undefined behavior to call it from one thread, while another thread is executing any of the following functions: std::fprintf , std::isprint , std::iswdigit , std::localeconv , std::tolower , std::fscanf , std::ispunct , std::iswgraph , std::mblen , std::toupper , std::isalnum , std::isspace , std::iswlower , std::mbstowcs , std::towlower , std::isalpha , std::isupper , std::iswprint , std::mbtowc , std::towupper , std::isblank , std::iswalnum , std::iswpunct , std::setlocale , std::wcscoll , std::iscntrl , std::iswalpha , std::iswspace , std::strcoll , std::wcstod , std::isdigit , std::iswblank , std::iswupper , std::strerror , std::wcstombs , std::isgraph , std::iswcntrl , std::iswxdigit , std::strtod , std::wcsxfrm , std::islower , std::iswctype , std::isxdigit .

POSIX also defines a locale named "POSIX" , which is always accessible and is exactly equivalent to the default minimal "C" locale.

POSIX also specifies that the returned pointer, not just the contents of the pointed-to string, may be invalidated by subsequent calls to setlocale .

Example

#include <clocale>
#include <cstdio>
#include <ctime>
#include <cwchar>
#include <iterator>
#include <string>
 
int main()
{
    // Make a "deep copy" of current locale name.
    std::string prev_loc = std::setlocale(LC_ALL, nullptr);
 
    // The C locale will be UTF-8 enabled English,
    // decimal dot will be German,
    // date and time formatting will be Japanese.
    if (const char* loc = std::setlocale(LC_ALL, "en_US.UTF-8"))
        std::wprintf(L"New LC_ALL locale: %s\n", loc);
    if (const char* loc = std::setlocale(LC_NUMERIC, "de_DE.UTF-8"))
        std::wprintf(L"New LC_NUMERIC locale: %s\n", loc);
    if (const char* loc = std::setlocale(LC_TIME, "ja_JP.UTF-8"))
        std::wprintf(L"New LC_TIME locale: %s\n", loc);
 
    wchar_t buf[100];
    std::time_t t = std::time(nullptr);
    std::wcsftime(buf, std::size(buf), L"%A %c", std::localtime(&t));
    std::wprintf(L"Number: %.2f\nDate: %Ls\n", 3.14, buf);
 
    // Restore the previous locale.
    if (const char* loc = std::setlocale(LC_ALL, prev_loc.c_str()))
        std::wprintf(L"Restorred LC_ALL locale: %s\n", loc);
}

New LC_ALL locale: en_US.UTF-8
New LC_NUMERIC locale: de_DE.UTF-8
New LC_TIME locale: ja_JP.UTF-8
Number: 3,14
Date: 日曜日 2022年11月06日 20時40分59秒
Restorred LC_ALL locale: C

See also

External links